Random 2D projected views of the example Magneticum galaxies for each of the six profile classes. For each galaxy, a box with a length of 200 kpc centred on the galaxy is shown, with the left plot showing the intensity map derived from all stars in the galaxy and the right plot showing the origin of the stars colour coded according to the in-situ/accreted fraction (with blue colours showing 100% in-situ fractions and red colours showing 100% accreted fraction). From left to right, top to bottom, the shown galaxies are from class A (upper left), class B (upper right), class C (central left), class D (central right), class E (bottom left), and class F (bottom right). As can be clearly seen, the amount of in-situ stars increases from the upper left class (A) to the lower right class (F).

Random 2D projected views of the example Magneticum galaxies for each of the six profile classes. For each galaxy, a box with a length of 200 kpc centred on the galaxy is shown, with the left plot showing the intensity map derived from all stars in the galaxy and the right plot showing the origin of the stars colour coded according to the in-situ/accreted fraction (with blue colours showing 100% in-situ fractions and red colours showing 100% accreted fraction). From left to right, top to bottom, the shown galaxies are from class A (upper left), class B (upper right), class C (central left), class D (central right), class E (bottom left), and class F (bottom right). As can be clearly seen, the amount of in-situ stars increases from the upper left class (A) to the lower right class (F).

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In the two-phase scenario of galaxy formation, a galaxy's stellar mass growth is first dominated by in-situ star formation, and subsequently by accretion. We analyse the radial distribution of the accreted stellar mass in ~500 galaxies from the hydrodynamical cosmological simulation Magneticum. Generally, we find good agreement with other simulatio...

Contexts in source publication

Context 1
... Class A: Extremely accretion dominated profiles. For these galaxies, the accreted stellar component is always dominant, even in the inner regions (see left panels of Fig. 1 and upper left panels of Fig. 3). About 7% of all galaxies show this kind of behaviour (see Tab. 1). Such galaxies have no clear transition radius between in-situ and accreted stellar ...
Context 2
... Class B: Accretion dominated profiles. For these galaxies, the fraction of in-situ and accreted stars near the galaxy center is equal, but for all larger radii the accreted fraction dominates (see middle panels of Fig. 1 and upper right panels of Fig. 3). This is a rare class, with only about 2% of all Magneticum galaxies in this class (see Tab. 1). It could also be interpreted as an extreme case of class A, but we here study it as a separate class. The transition radius for these galaxies is very small, and is not a real transition in all cases as the in-situ component does not ...
Context 3
... Class C: Classic profiles. The inner regions of these galaxies are dominated by in-situ formed stars, while in the outskirts the accreted stellar component is dominant (see right panels of Fig. 1 and central left panels of Fig. 3). This is by far the most common class of profiles, with 72% of all Magneticum galaxies showing this behaviour (see Tab. 1). This is also the behaviour found most commonly in previous work for example by Cooper et al. (2010); Rodriguez-Gomez et al. (2016); Pulsoni et al. (2020). These galaxies have a clear transition radius from ...
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... Class D: Double cross-over profiles. These galaxies have a large accreted fraction dominating in the inner and the outer regions, with their intermediate-radii regions dominated by in-situ formed stars (see left panels of Fig. 2 and central right panels of Fig. 3). 13% of all Magneticum galaxies fall in this category (see Tab. 1), making this the second most common profile type. Given its nature, these profiles have two transition ...
Context 5
... Class E: Balanced profiles. A small fraction (≈ 4%, see Tab. 1) of all Magneticum galaxies reveal profiles for which the in-situ and accreted contributions are nearly equal over a large radial range (see middle panels of Fig. 2 and bottom left panels of Fig. 3). For these profiles, we usually find a transition radius at very large radii, however, even if the outer parts are slightly dominated by accreted stars, the fraction of accreted stars usually stays below ...
Context 6
... Class F: In-situ dominated profiles. Galaxies in this class have radial density profiles that are always dominated by in-situ formed stars at all radii, even at their outskirts (see right panels of Fig. 2 and bottom right panels of Fig. 3). Only 2.7% of all Magneticum galaxies show this behaviour, with the in-situ fraction always larger than the accreted fraction (Tab. 1). As for class A galaxies, there is no transition radius for these ...
Context 7
... of the assembly history for the six classes are given in the lower panels of Fig. 1 and Fig. 2, with the history always belonging to the galaxy for which the radial density profiles are shown in the upper panels of the same figures, and the intensity maps are shown in the according panels of Fig. 3. The redshifts of past merger events are marked as red/green/blue dashed lines for major/minor/mini mergers, respectively. These six examples show that all galaxies, but one, experience major mergers, with the galaxy that experiences no major merger being of class C. In the case of the example galaxies from classes A and B (the ...

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